1. Field
The present disclosure relates to sound technology in general and, in particular, relates to waveguides and speaker assemblies having multiple apertures.
2. Description of Related Art
Speakers convert electrical signals to sound waves that allow listeners to enjoy amplified sounds. One of the factors that determines the quality of the speaker-generated sound heard by the listener is the sound pressure level (SPL). The quality of the SPL generally depends on the size of the speaker relative to the distance between the speaker and the listener. Generally, a larger distance requires a larger speaker size. Obviously, there is a practical limit on how large a speaker can be made. For example, an overly large speaker may create difficulties in transporting or mounting. Furthermore, a correspondingly large driving element needed to drive a large speaker may require an impractical amount of power.
To circumvent such drawbacks, an array of smaller sized speakers can be used to achieve similar acoustic results. As is generally understood, sound waves from each individual smaller sized speaker may combine to yield a combined sound wave that behaves similar to a sound wave emanating from a single large speaker.
Effective and coherent combination of sound waves may be achieved when certain wave related parameters are satisfied. One such requirement is that individual waves emanating from the smaller sized speakers exhibit a substantially fixed phase difference relative to waves output from the other smaller sized speakers. When all of the smaller sized speakers in a linear arrangement are driven substantially in phase (substantially zero phase difference), a resulting combined wave propagates in a direction normal to a line defined by the speakers. A substantially fixed non-zero phase difference among the individual waves results in a combined wave that propagates at an angle with respect to the normal direction. In typical arrayed speaker applications, individual smaller sized speakers are driven substantially in phase.
Another requirement for a quality combined wave from the array of smaller speakers includes setting the spacing between speakers to certain dimensions relative to sound wave wavelengths. As a rule of thumb, it is generally accepted that the spacing between two neighboring speakers must be smaller than the wavelength of an output sound wave to generate a combined wave. In some instances, it may be desirable for the spacing to be within half the wavelength of a particular sound wave. One reason for the requirement may be due to instances when the spacing is larger than a wavelength (or half the wavelength), wherein the resulting combination of the waves suffers from poor directional properties including unwanted side lobes of sound patterns away from the desired direction.
The wavelength of a wave may be determined as wave velocity divided by wave frequency. The wave velocity of sound in room temperature air is approximately 1130 ft/sec. For an exemplary low frequency audio sound having a frequency of 200 Hz, the corresponding wavelength is approximately 68″. Similarly, a midrange audio sound with a frequency of 2000 Hz, the corresponding wavelength is approximately 6.8″. For low frequency audio sound, a spacing between the speakers that is less than the wavelengths under the exemplary 68″ is easily achieved. For midrange audio sound, arranging the midrange speakers with spacing under the exemplary 6.8″, while more challenging than that of the low frequency case, is still achievable.
For a high frequency audio sound, a relatively small wavelength poses a problem for spacing of high frequency speakers, since the components of the speaker have physical limitations on how small they can be made. For example, a magnet assembly that drives a speaker cone needs to be a certain minimum size. As a result, positioning two of such speakers adjacent to each other yields a center-to-center spacing that suffers from directionality problems. Thus, a resulting high frequency sound emitted from a conventional array of high frequency speakers can suffer from the aforementioned directionality problems.
For the foregoing reasons, there is a continuing need for an improved system and method for transmitting a sound wave from a speaker or a plurality of speakers. In particular, there is a need for transmitting sound waves in a manner that allows for increasing of the dimension of the transmitted wavefronts while mitigating the undesired effects that degrade the sound quality, and allows for dimensions of the speaker assembly to be reduced.